Signal generators used in fiberoptic technology, typically semiconductor lasers, are highly sensitive to light reflected back into the signal generator. Reflected light causes instability in the laser and noise in the signal. Thus, optical isolators were developed. Optical isolators transmit light in the direction of propagation of the signal, but block reflected light traveling opposite to the direction of propagation of the signal.
Typical optical isolators are comprised of a first collimator, a core assembly, and a second collimator. The first collimator holds an input optical fiber, while the second collimator holds the output optical fiber. The core assembly is typically comprised of a first polarizer, a faraday rotator, and a second polarizer.
Currently, optical isolators are subject to several constraints. First, the ratio of insertion loss to return loss must be low. Insertion loss is the loss in intensity of the signal as it propagates forward through the optical isolator. Return loss is the loss in intensity of any light, primarily reflected light, traveling opposite to the direction of propagation of the signal. Insertion loss and return loss of optical isolators are primarily determined by the insertion and return losses of the collimators. Lower insertion loss requires good alignment of each collimator's components. Return loss is raised by ensuring that the components of each collimator are clean or smooth.
Another constraint in the utility of optical isolators is their ability to be used in a variety of environments. One method of affixing the collimators uses epoxy. However, epoxy is damaged when subjected to drastic temperature changes. Consequently, the optical isolator cannot withstand variations in the environmental conditions.
Soldering techniques have been used to affix the collimators to the holders in place of epoxy in order to provide a collimator better able to function in a variety of environments. However, soldering introduces several problems. High temperature solders damage the alignment of collimators. Low temperature solders are expensive and provide weaker bonding than high temperature solders. Some solders also require flux, which contaminates collimator components, thereby increasing insertion loss.
In order to optimize performance of the optical isolator, the isolation peak position should be adjustable. Thus, the core should be modifiable in order to provide the optimal isolation peak position.
Finally, commercial use of optical isolators is limited due to their cost. Typical optical isolators achieve the requisite alignment, cleanliness, and mechanical characteristics only at great expense.
Accordingly, what is needed is a system and method for an optical isolator having the requisite ratio of insertion loss to return loss, mechanical characteristics, environmental flexibility, and the ability to optimize performance. It would also be beneficial if such an optical isolator could be provided at lower cost. The present invention addresses such a need.